Perlite, production of perlite aggregate for insulation , filtration and horticultural
Perlite/silicate composites for high temperature insulation and formed shapes
Both flat rounded of socium silicate perlite insulation
Perlite/silicate composites
Expanded Perlite granules can be bonded to form rigid shapes for a very wide range of applications. The most suitable binder for many purposes is a liquid sodium silicate similar to traditional "water glass." The liquid sodium silicates are solutions of water soluble glasses manufactured from varied proportions of Na2C03 and SiO2, providing a wide range of chemical and physical properties.
Sodium silicates are widely used as high temperature adhesives and binders due to the following properties:
- Low Cost
- Inorganic
- Easy to Handle
- Rapid Controlled Set
- High Strength
- Insolubility (when aired)
- Chemical Stability
Silicate-bonded Perlite makes an insulation material which is completely non-flammable, the refractory nature of the bond being a major advantage.
Potassium silicate is sometimes preferred for applications where heat insulation and fire resistance are the main objectives. This material has a slightly higher softening point than its sodium counterpart.
Sodium silicate is widely used as a binder for molding sand in foundries. The technology for Perlite/sodium silicate composite manufacture is based largely on this foundry industry experience.
| TYPICAL PROPERTIES OF PERLITE/SODIUM SILICATE COMPOSITES | |
|---|---|
| Thermal Conductivity at mean temp. 120°C | 0.058 W/m.K |
| Thermal Conductivity at mean temp. 230°C | 0.081 W/m.K |
| Thermal Conductivity at mean temp. 350°C | 0.094 W/m.K |
| Thermal Limit (ASTM C-447) | 650°C |
| Density ASTM C-447) | 180-260 kg/m3 |
| Modulus of Rupture (ASTM C-203,C-446) minimum | 0.34-0.41 N/mm2 |
| Compressive Strength(ASTM C-165) minimum | 0.52-0.61 N/mm2 |
| Linear Shrinkage (ASTM C-356) | less than 2% at 650 °C |
| Water Absorption | under 10% by volume after 24 hours |
Perlite/sodium silicate technology
A wide range of formulations of Perlite, sodium silicate solution and setting agent can be used, together with additives to control setting of the mix. General guidelines are given as a starting point.Soluble silicate grades
The choice of grade of sodium silicate solution depends on the application and setting process being used. Generally, a higher silicate to alkali ratio gives faster setting while lower ratios and higher solids contents give greater strength in the finished product.Setting agents
- Gas Carbon dioxide (usually blown through the molded shape)
- Liquids Glycerol Diacetat plus either
- Glycerol Triacetate
or - Ethylene Glycol Diacetat
- Solids
- Solids Calcium silicates - e.g. Portland Cement
- Calcium Sulphate - e.g. gypsum
- Silicides-g.g. Ferrosilicon or Calcium Silicate
- Silicofluorides or fluorosilicates
- Ground metallurgical slab
- Heavy metal salts-e.g. carbonates or phosphates
| Setting Process | Silica/Alkali Ration | Solids Content % |
| Gas Injection | 2.00--2.50:1 | 43-50 |
| Liquid Hardeners | 2.50--2.90:1 | 40-45 |
| Solid Hardeners | 2.00--2.30:1 | 45-50 |
| SUGGESTED FORMULATIONS USING DIFFERENT SETTING AGENTS | |||
|---|---|---|---|
| Material* | Gas Setting | Liquid Setting | Solid Setting |
| Sodium silicate solution as % by volume of Perlite | 2.5-5% | 5-10% | 5-15% |
| Setting agent as % by weight of sodium silicate | 15-25% at 20°C | 8-14% | 25-50% |
| (*amount of silicate needed will depend on the particle size, density, and absorbency of the Perlite used.) | |||
| APPLICATIONS OF PERLITE/SILICATE COMPOSITES | |||
|---|---|---|---|
| High Temperature Insulation | Fire Protection | Building Construction | Other Applications |
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